Electro-initiating device



y 2. 1968 w. E. PERKINS ET. AL 3,390,636

ELECTRO-INITIAT ING DEVICE Filed Nov. 17, 1966 WILLIAM E. PERKINS GEORGEF? CATRAMBONE United States Patent 3,390,636 ELECTRQ-INITTATING DEVICEWilliam E. Perkins, Runnemede, N.J., and George P. Catrambone,Warminster, Pa., assignors to the United States of America asrepresented by the Secretary of the Army Filed Nov. 17, 1956, Ser. No.595,275 11 Claims. (Cl. 10228) ABSTRACT OF THE DISCLOSURE A device forinitiating an explosive which will be insensitive to initiation by radiofrequency radiations or electro-static discharges. The device includesan electrode, housed in a metallic body, adjacent an iniziating meanscomposed of carbon (graphite), red phosphorus (stabilized) and bariumnitrate.

The invention described herein may be manufactured and used by or forthe Government of governmental purposes without the payment to us of anyroyalty thereon.

This invention relates to an electro-initiating device and moreparticularly to an electro-initiating device which is insensitive toinitiation by radio frequency and electrostatic discharges.

In prior art initiators, it is common to provide an electrical means forinitiating an explosive which, in turn, ignites the main charge.

For more than a decade, ordnance items containing electro-explosivedevices (EED) have caused deep concern because of malfunctions causedprincipally by RF radiations and electro-static discharges. Thesemalfunctions have been manifested primarily by premature firing, byfiring later than desired, and in some instances, misfiring.

Some early EED contained conductive priming compositions, but many ofthese were found to be too sensitive. One of the many approaches insolving this problem was to incorporate bridge wires in the BBB. It wasfound that the conductivity of the Wire had to be considered to copewith the RF problem, and even low-resistance bridge wires, safe enoughto pass RF energies without firing, were dudded.

Limited success realized in bridge wired EED resulted in a shift toexploding bridge wired devices (EBWs). Although these EBWs wererelatively safe to RF radiations, they could be actuated prematurely byelectro-static discharges. This deficiency, and the fact that largepower packages are required to fire them, has made them somewhatundesirable for ordnance applications.

Numerous other approaches have been considered; i.e., attenuators,filters, and auxiliary electrical device, but none olfer a completesolution and each add to the complexity and hence reduce the reliabilityof the BED.

The present invention describes conductive mix electric ignition elementcapable of functioning under service conditions of 65 F. to +350 F. froma prescribed firing pulse while being considered safe to inadvertentactuation from radio frequency (RF) signals and electro-staticdischarges.

It is therefore an object of the present invention to provide anelectro-initiating device which is insensitive to initiation by radiofrequency radiations.

Another object is the provision of an electro-initiating device which isinsensiitve to initiation by electro'static discharges.

A further object is to provide an electro-initiation device utilizing anon-corrosive conductive composition.

Still another object is the provision of an electro-initiatice ingdevice for firing an explosive charge in response to an electricalimpulse.

The above objects as well as others together with the benefits andadvantages of the invention will be apparent upon reference to thedetailed description set forth below, particularly when taken inconjunction with the drawing which shows a sectional view of theinvention.

As can be seen in the drawing, an electro-initiating device 10 consistsof a hollow cylindrical electrically conductive metallic body 12, whichhouses an electric conductor or electrode 14, an initiating charge 16and a supplemental charge 18. Electrode 14 is composed of a metallicsubstance e.g., stainless steel, not readily oxidized over the operatingtemperature range. The initiating charge 16 is composed of carbon(graphite), red phosphorus (stabilized), and barium nitrate. Thesupplemental charge 18 could be an igniter, detonator or the like,depending upon the application of the device.

An electric insulator 20 is interposed between body 12 and electrode 14,and may be glass, ceramic or material of good dielectric and mechanicalstrength. A metallic support cup 22 houses supplemental charge 18between a pair of retaining discs 24 and 26, the disc 26 being securedin body 12 by a crimp 28. Discs 24 and 26 may be magnesium, aluminum, orthe like.

In operation, an electric current travels from a source (not shown)through a firing switch (not shown) into electrode 14. After theelectrode 14, the current passes through initiating charge 16 therebyigniting the supplemental charge 18 through the retaining disc 24 andthe main charge (not shown) of the ordnance item (not shown). Thecurrent then travels back through the conductive body 12 to theelectrical source thereby com pleting the circuit.

As an example, the following requirements might be necessary indeveloping a bomb ejector cartridge having an EED which would:

(1) Be stable over the temperature range of 65 F. .to +350 F.

(2) Be capable of passing 1 ampere of current and/or watt for 5 minutesover the temperature range without firing.

(3) Be capable of firing prior or subsequent to conditions of (2) from acurrent of 5 amperes in less than 25 milliseconds.

(4) Be non-corrosive.

(5) Ignite propellant adequately.

(6) Exhibit an open circuit after firing to avoid drain on the powersupply.

(7) Be safe from actuation via electro-static discharges.

The following combination meets the abovementioned desired requirements:

(1) Conductive mix-stabilized red phosphorus, 23% by weight, bariumnitrate, 69.5% by weight, graphite, 7.5% by weight.

(2) Charge weight-3.5 grains.

(3) Loading pressure1500 psi.

(4) Conductive gap (shortest distance through the mix between theelectrode and the body)0.20 inch.

(5) Resistance2.7 ohms +0.3 ohms (from R=E/I relationship at 1.0 ampere(for 5 minutes) over temperature range -65 F. to +350 F.).

(6) Functioning time-less than 25 milliseconds when fired at 5 amperes.

(7) Output-equivalent to primers containing 3.5 grams.

(8) Electro-static sensitivityinsensitive to discharge of 150,000 ergesor less.

(9) Non-corrosiveness-equivalent to non-corrosiveness claimed for otherred phosphorus/barium nitrate priming compositions.

t c 10) Open circuit requircmentswnen tired. the components areapproximately as electrically conductive as the uncharged component.

An electric ignition element with satisfactory insensitivitycharacteristics to current RF and electro-static hazards has beenattained using the non-obvious conductive miX approach.

The electro-initiating element will not prematurely function fromelectrical currents up to l.0 ampere tor periods of 5 minutes or less.With changes in iormulation, loading pressure. and gap widths thesensitivity characteristics can be altered to make theelectro-initiating device more or less sensitive, l.e. no-tire currentcan be controlled at less than or more than l.0 ampere. Specifically, ithas been established that increases in percentages of conductivematerial in the composition and an increase in the loading pressurestend to decrease sensitivity. while an increase in the gap width tendsto increase sensitivity, i.e., fire at lower current levels.

The sensitivity of the electrode-initiating device IS a function of itsconductivity.

Conductivity can be increased by increasing the graphite content,increasing the loading pressure. and/or decreasing the gap, andconversely, the conductivity can be decreased by decreasing the graphitecontent. decreasing the loading pressure, and/or increasing the gapdistance.

Due to the negative temperature coetficient or sensitivity of graphite,compositions can be formulated which are more insensitive at highertemperatures and more sensitive at lower temperatures for use in unusualapplications.

Obviously many modifications and variations or the present invention arepossible in light or the above teachings. It is therefore to beunderstood. that within the scope of the appended claims. the inventionmay be practiced otherwise than as specifically described.

We claim:

1. In an electro-initiating device for detonating an emnance item havinga main charge and comprising a hollow cylindrical conductive body havingtwo epen ends,

an electrode housed in one of said ends.

a supplemental charge housed in the other or said ends.

and

initiating means within said body between 5310 electrode and saidsupplemental charge.

the improvement wherein said initiating means consists of a compositionof stabilized red phosphorus. barium nitrate and graphite in suchproportions as will not prematurely function from electrical currents upto 1.0 ampere for periods of five minutes max.

2. An electro-initiating device of the type described in claim 1 whereinsaid initiating charge is characterized by being insensitive todischarge of 150.000 ergs max.

3. An electro-initiating device of the type described in claim 1 whereinsaid initiating charge is characterized by 4 being stable over thetemperature range of 65 F. to 350" F.

ll. An eiectro-initiating device of the type described in claim lwherein said initiating charge is non-corrosive.

it. An electro-initiating device of the type described in aim 1 whereinsaid initiating charge is characterized by insensitive to electro-staticdischarges.

An electro-initiating device of the type described in claim 1 whereinsaid initiating charge is characterized by being insensitive to radiofrequency radiations.

I An electro-initiatirig device of the type described in claim 1.ivnerein said initiating charge consists of a composition or 13% byweight stabilized red phosphorus, t1i9.5% by weight barium nitrate and7.5% by weight graphite.

ll. An eiectro-initiating device of the type described in claim l.wherein said supplemental charge is housed in .l metallic support cupand secured therein by a pair of retaining discs.

it. An eiectro-initiating device of the type described in im l. whereinsaid electrode is separated from said conductive body by an insulatorthereby directing the current irom iald electrode to pass through saidinitiative charge before going out through said conductive body.

l0. An electro-initiating device of the type described in claim 3wherein said electrode is composed of a metallic .itubstance not readilyoxidized over said .temperature cringe.

Ill. An electro-initiating device comprised of c hollow cylindricalconductive body having two open ctids,

an electrode housed in one of said ends,

an insulator separating said electrode from said con- ..luctive body,

ct metallic support cup housed in the other of said ends,

ct pair of retaining discs secured in said metallic support cup.

.t supplemental charge housed in said pair of retaining cliscs.

initiating means within said body between said electrode crud saidsupplemental charge, comprised solely of a composition of about 23% byweight stabilized red hosohorus, b5% by weight barium nitrate, and

% by weight graphite.

lli leferences Cited UNITED STATES PATENTS llli.b45.57l c'l953Silverstein 149-30 1.696.191 12;1954 Sheehan 10246 X Ii,320.l04 r'l967Stadler et al 149-43 X .i DREIGN PATENTS 015.040 ll/1960 Great Britain.

lillENJAMIN A. BORCHELT, Primary Examiner.

W'ERLIN PENDEGRASS, Examiner.

